In the field of silver halide color photographic light-sensitive materials, it has conventionally been desired to raise sensitivity and image quality of the light-sensitive materials. This tendency has been particularly remarkable in recent years. In general, however, higher sensitivity requires to use of silver halide grains having larger grain size, and hence attempts to raise sensitivity have inevitably encountered the problems of deterioration of graininess and reduction of gamma. Therefore, techniques for imparting good graininess and high gamma while maintaining high sensitivity have been strongly desired.
One technique for obtaining high gamma while keeping high sensitivity is to narrow the grain size distribution of emulsion grains. For example, mono-dispersed emulsions as disclosed in British Patent No. 1,469,480 or Japanese Patent Application (OPI) No. 142,329/80 (corresponding to U.S. Pat. No. 4,301,241) can provide a high gamma. (The term "OPI" as used herein refers to a published unexamined Japanese Patent Application.) In addition, another effective technique for obtaining a high gamma is to make development initiation of every grain uniform by minimizing the difference in halide composition between grains. Thus, an approach of making an emulsion mono-dispersed and narrowing iodide distribution between grains has been made, for example, as described in Japanese Patent Application (OPI) No. 153,428/77 (corresponding to U.S. Pat. No. 4,150,994).
Further, in order to obtain good graininess while keeping high sensitivity, it is necessary to increase the number of grains to be developed. In general, mono-dispersed emulsions contain more developable grains than poly-dispersed emulsions at a certain exposure amount or less than that, thus providing better graininess.
However, it is known that, since mono-dispersed emulsions generally have such a narrow size distribution that they have a narrow exposure latitude and, in a high exposure region, they do not necessarily give better graininess than poly-dispersed emulsions having the same mean grain size. In order to overcome this defect, an approach has been employed of incorporating several kinds of mono-dispersed emulsions different from each other in mean grain size in different layers to form a multi-layer coating or, as is disclosed in Japanese Patent Application (OPI) No. 178,235/82 and 72,440/84 (corresponding to U.S. Pat. Nos. 4,446,228 and 4,481,288, respectively) to use these emulsions as a mixture in the same silver halide emulsion layer.
However, the present inventor has found that in order to obtain the same exposure latitude, higher gamma, and excellent graininess while keeping sensitivity by using only mono-dispersed emulsions as described above, in comparison with poly-dispersed emulsions having as large a mean grain size as 1.3 .mu.m or more (this size is generally desired in high sensitivity color photographic materials), three or more mono-dispersed emulsions different from each other in mean grain size must be prepared and separately multi-coated, or must be mixed in an appropriate ratio to use in one and the same emulsion layer. This technique is far from practical use due to its complexity.
As is mentioned above, the conventional techniques of using mono-dispersed silver halide to improve graininess and gamma of high speed silver halide color photographic light-sensitive materials are not totally satisfactory, since it is effective only in limited exposure region, or are too complicated to practice.